1. Field of the Invention
The present invention relates to a water based ink composition for a free ink rollerball pen, more specifically to a water based ink composition for a free ink rollerball pen in which the visible color of ink liquid is almost consistent with the visible color of drawn lines in writing on a sheet of white paper by adding white resin particles insoluble in the aqueous medium to the ink composition comprising a dye and an aqueous medium.
2. Description of the Related Art
A free ink rollerball pen is of a structure in which ink is filled directly into an ink reservoir without using an ink absorber such as a fiber bundle.
A conventional water based ink composition for a free ink rollerball pen is prepared by dissolving a dye or a pigment, a rust preventive, a preservative, a lubricant, a pH controller, a drying preventive, a thickener and the like in water and a solvent, and inks further containing high molecular fine particles for various purposes are proposed. It is disclosed in Japanese Patent Application Laid-Open No. Sho 63-256669 that white, colorless or colored spherical resin particles having a particle diameter of 10 to 1000 nm which are insoluble in a liquid medium for ink and do not form a film are used in order to allow the ink to be discharged smoothly and prevent skipping of the drawn lines in writing. A water based ink for a ballpoint pen containing high molecular spherical fine particles (particle diameter: 50 to 600 nm) for the same purpose is disclosed as well in Japanese Patent Publication No. Hei 5-46389. Also, it is described in Japanese Patent Application Laid-Open No. Sho 58-176281 that a water based ink containing a styrene-butadiene latex emulsion has thixotropy and imparts gloss, luster and water resistance to drawn lines. Further, disclosed in Japanese Patent Application Laid-Open No. Sho 59-140273 is a water based ink for a ballpoint pen in which a high molecular dye prepared by combining a water-insoluble polymer having an amino group with an anionic dye or a reactive dye is used and which is improved in water resistance, intensity of the color, feathering and drying property. Also, in order to obtain an ink for ink jet recording which has a low viscosity and is capable of high intensity recording, disclosed in Japanese Patent Publication No. Sho 60-42832 is an ink in which a hydrophobic dye solution and fine particles which are of a polymer prepared by emulsion-polymerizing a vinyl monomer are dispersed in an aqueous medium, wherein the fine particles swell in a solvent for the hydrophobic dye and are insoluble and do not swell in water, and disclosed in Japanese Patent Publication No. Sho 60-42833 is an ink further containing a water-soluble dye in addition to the above ink. In these publications, the water based inks having intense colors are obtained by impregnating polymer fine particles with dyes and using dye aqueous solutions in addition thereto. Further, proposed in Japanese Patent Publication No. Hei 1-29829 is a writing medium composition in which a carboxylated styrene-butadiene latex emulsion is added. In this composition, the above latex is used as latex having weak adhesive force and no permeability to a writing surface for the purpose of erasing the lines.
Incidentally, one of the characteristics of a free ink rollerball pen is that the remaining amount and the color of the ink can be confirmed from the outside of the holder. The visible color of an ink liquid is important as a standard for judging the visible color of the drawn lines in writing on a sheet of white paper. As described above, either a pigment ink or a dye ink is used for an ink composition for a free ink rollerball pen. In the case of the pigment ink, the visible color of the ink liquid is close to that of the drawn lines in writing on a sheet of white paper. However, it is difficult in terms of dispersion stability to tone the color by mixing different kinds of pigments, so that the kind of the color is restricted.
In contrast with this, in the case of the dye ink, there is an advantage such that the color can readily be toned as compared with the pigment ink, but there is a disadvantage such that the visible color of the ink liquid is not so close to the visible color of the drawn lines in writing on a sheet of white paper, so that the color written on a sheet of paper can not definitely be confirmed from the color of the ink liquid. Accordingly, there has been a problem in that when a free ink rollerball pen is charged with a dye ink, it is difficult to know definitely the color of the ink written on a sheet of paper from the appearance. No mentions of this matter are found in the descriptions about the inks using the fine polymer particles mentioned above, and it has been desired to solve the matter. Viewing from such a standpoint, an object of the present invention is to provide a water based dye ink composition for a free ink rollerball pen in which it is made possible to allow the visible color of the ink liquid to be almost consistent with the visible color of the drawn lines in writing on a sheet of white paper when using a dye ink and in which the color can be toned in various ways.